1. Field of Invention
The present invention relates to a tissue papermaking machine for manufacturing a tissue paper web, comprising:                a wet section for forming a fibre web,        a press section for pressing the fibre web, said press section comprising:                    a single press, comprising:                            a first press element,                a second press element, said press elements forming a press nip therebetween with a predetermined pressure,                a press felt running in an endless loop around a plurality of guide rolls and through said press nip together and in contact with the formed fibre web, the second press element being arranged inside the loop of the press felt,                a smooth belt running in an endless loop around a plurality of guide rolls and through said press nip together and in contact with the formed fibre web, the first press element being arranged inside the loop of the belt, and                a transfer roll arranged inside the loop of the smooth belt,                                    a dry section for final drying of the fibre web pressed in the press nip, said dry section comprising a drying surface for final drying of the pressed fibre web,said transfer roll being arranged to form a transfer nip together with the drying surface for transfer of the fibre web to the drying surface, whereby the smooth belt is arranged to carry the pressed fibre web between the press nip and the transfer nip.                        
The present invention also relates to a method for manufacturing a tissue paper web in a tissue papermaking machine with higher bulk and softness than what is obtained by a conventional method, said method comprising the steps:                a fibre web is formed and pre-dewatered in a wet section,        the fibre web is pressed in a press section, comprising:                    a single press, comprising:                            a press nip,                a press felt running in an endless loop around a plurality of guide rolls and through said press nip together and in contact with the formed fibre web,                a smooth belt running in an endless loop around a plurality of guide rolls and through said press nip together and in contact with the formed fibre web, and                a transfer roll arranged inside the loop of the smooth belt,                                                the fibre web pressed in the press nip is finally dried in a dry section comprising a drying surface for final drying of the pressed fibre web,wherein the fibre web is transferred to the drying surface by means of a transfer nip formed by the transfer roll and the drying surface, and wherein the pressed fibre web is carried between the press nip and the transfer nip by the smooth belt.        
The present invention also relates to a method for reducing the energy consumption in a tissue papermaking machine of the above-mentioned type, and a method of rebuilding a conventional machine. The invention also relates to a use of the smooth belt for manufacturing a relatively high-bulk and very soft, creped tissue paper web.
By conventional tissue paper is meant herein soft paper with a grammage usually under 25 g/m2, e.g., 15-25 g/m2, and bulk from 6 to 8.8 cm3/g depending on the grammage. Tissue paper is the base paper for several single-ply and multiple-ply paper products, such as napkins, hand towels, and rolls of toilet paper, and it has a bulk within the range of 7-10 cm3/g and a softness better than that of conventionally produced tissue paper. Tissue paper which is produced according to the invention has a grammage of 12-42 g/m2, preferably 15-25 g/m2, thickness of 130-240μ, MD strength of 60-500 kN/m, CD strength of 40-250 kN/m and a bulk of 7-10 cm3/g. The pulp used can preferably be a mixture of 70% short fibres and 30% long fibres. The pulp can be “virgin”, which is fresh pulp from pure cellulose and a mixture of hardwood pulp and softwood pulp, i.e., short and long fibres. Other types of pulp can also be used, e.g., recycled fibres, in the method and the tissue papermaking machine according to the invention. Different pulps are used for different products. For a pulp for making toilet paper, facial tissue and the like a pulp is used which is a mixture of 50-90% hardwood and 50-10% softwood. For towels, the pulp contains 0-50% hardwood and 100-50% softwood.
By relatively high bulk is meant a bulk of soft paper lying in said range of 7-10 cm3/g. The paper has a thickness lying in the range of 130-240μ, said thickness being measured prior to converting. The softness can be up to 90 on the TSA scale of 0-100.
2. Description of Related Art
FIG. 3 of U.S. Pat. No. 6,743,339 shows a tissue paper machine according to the preamble of claim 1, i.e., where a smooth and essentially impermeable belt runs together with the tissue paper web through the single press in the pressing section of the tissue papermaking machine and further to a transfer nip against a drying surface. The problem with this machine configuration, however, is that it has very bad runability because too much water is entrained with the press felt in the nip and so-called crushing of the tissue fibre web can occur in the press nip. One solution to this problem is to reduce the pressure in the press nip and at the same time compensate for the resulting reduced dewatering by introducing one or more additional press nips in the press section. Such machine configurations are described in FIGS. 1, 2 and 4 of said specification. However, this solution has the drawback of making it hard to create sufficient bulk, i.e., thickness, of the tissue fibre web, since each press nip which the tissue fibre web has to go through negatively affects the bulk by producing more fibre clusters in the web and makes it hard to achieve a final product of requisite quality.
In U.S. Pat. No. 6,287,426 B1 a tissue paper machine is described, comprising a smooth belt that runs in a loop through a press nip and from which the web is transferred to a clothing, which carries the web further to a transfer nip in the drying section.